[William]

A couple of possible plot devices:

UNAM (National Autonomous University of Mexico) is a unique sort of university, with wide-open admission policies and a student population numbering a quarter million. It would make a fine setting for various kinds of scenes, or even as a base of operations for one or more characters.

Consider gang activity (possibly spurred by events in the news) as an angelic-infernal battleground. Gangs are prominent in the drug trade and the illicit immigration routes, both ripe for infernal infestation: Fleurity and Mammon would both find the industry appealing. Angels willing to take on long odds can engage this turf; David, especially, is known to work with gangs. His agents can become disturbingly supportive of organizations they infiltrate, and the tension between Role, morality, and loyalty to long-time comrades could make for great drama.

There are a number of colorful characters in Mexican current events that you could interpret in different ways; Subcomandante Marcos of the Zapatista rebels comes to mind. (The self-proclaimed non-leader of an ultra-left-wing "post-modernist" armed non-violent rebellion? I'm not sure whether I smell Lilith or Novalis. Maybe both. (Novalis smells like lots of flowers, of course. Lilith? ^_^ She schmells gooot. Hy mean, really goot....))

A third colorful group to introduce in the setting would be the Santeria pantheon; presumably, these are the same as the Voodoun loa, who are granted passage on Earth by Heaven. The religion is deeply entangled with Catholicism in Mexico, probably much to the dismay of Laurence. Presumably, however, this means that they're reasonably likely to be on Heaven's side most of the time. Given the proliferation of enemies discussed above, Heaven could even be grateful for the assistance...